golangci-lint round #3

this is the third round of preparing to use the golangci-lint on our
code base.

Signed-off-by: baude <bbaude@redhat.com>

cmd/podman/diff.go

@@ -136,5 +136,5 @@ func diffCmd(c *cliconfig.DiffValues) error {
 	} else {
 		out = stdoutStruct{output: diffOutput}
 	}
-	return formats.Writer(out).Out()
+	return out.Out()
 }